My post won't help you decide, but my hope is that smiths get better tank items to make in the expansion, and I hope that most are BOE.
Correct me if I'm wrong, but most of the smithing items in this expansion were DPS items (and BOP) that could be adapted to be tank items with gems or chants. Why couldn't each DPS item have a tank version like the way Engineers could make [item]Tankatronic Goggles[/item] and [item]Furious Gizmatic Goggles[/item].
from the most part, the new BSMITH stuff in wotlk isn't spec specific (O_o). You should be able to make most of them without worrying about that.
For now, if you want a solid tanking weapon without relying on drops (trust me it sucks using grom'tors for 6 months) than swords is an awesome way to go, especially if you get lots of badges from heroics all the time you can easily get the t3 one and boom, you won't replace it till Mallet or BT. If you like pvp, mace is still great, Stormherald is still a very good weapon for PvP warriors so go that route if you love it. If you want to get a very good tanking or pvp chest, then armorsmith you can't go wrong, like seriously the tanking capabilities of it is great, threat, hp, oh-shit button, and good armor. Not to mention it'll help with the wotlk updates to str better than most of the PvE tanking chests.
You asked about blacksmithing so I won't comment on Engineering. The sword is actually good. It should be almost trivial to upgrade it to [item]Blazefury[/item] at this point. The breastplate seems really nice, my reservation on it is that there is a very good badge chest available for 100 badges. Whether it would be more work to get 100 badges, or to upgrade the chest to the T3 version is something you would have to decide. It's the only item you can make as an armorsmith, so something to think about.
Kaze has a good point as the tanking chest is on par with the T5 chestpiece for warriors for tanking. I personally would disagree however because of the ease with which you can replace the chest vs. the weapon. The bulwark of ancient kings (the T3 of chest) is replaced in tanking terms by the chestplate of stoicism (100 badges) and if you pvp alot the S2 has alot of resil on it which proves to be a very worthwhile stat even with the loss of some others. The sword on the other hand doesnt get replaced until T5 with no other purchasable options around. You can hope for some T4 drops that are sidegrades or some heroic Magisters Terrace sword which would be a threat weapon but almost nothing else. Depending on the content you are doing or plan on doing, the sword is much harder to replace for most.
If you are PvPing, you won't find a better chest with S2. S3 is a side-grade. S4 is an upgrade. The only reason I'd consider getting the S2 or S3 chest is if I was hurting for resilience on a 2v2 team.
The armorsmithed chest is a lot cheaper to make than Blazefury (less vortexes), and will be your #1 threat and EH chest until T6. It has more threat and EH than the 2.4 badge chest (although the badge chest is better for avoidance fights).
Personally, though, I spent a lot more time off-tanking and DPSing (and now I'm full-time fury), so I gemmed my chest with 3x str gems, and don't regret it at all. For PvE DPS, it's better than the S3 due to the amount of hit vs armor pen (until you get high armor pen), and the badge fists are clearly better than anything a weaponsmith could make.
One additional thing that came out today about WotLK was interesting and somewhat pertinent here. Bliz is at least tossing around the idea of allowing weaponsmiths to add sockets to weapons, and allowing armorsmiths to add a meta-socket to armor.